To preemptively answer the question "why do you want it / what is it
you're trying to achieve", I have a log of a dhcp conversation which
contains what I think is a repeated DHCPDISCOVER stanza. Rather than
the manual copy/paste/diff cycle, I'd like this tool to look at the
log and tell me: "Yup, you've got a stanza/paragraph repeated 4
times".

You may want to take a look on logcheck package or write your own perl/awk program